Posted 08-06-2003 at 04:37:33
[Reply][Send Email]most old houses around here are built close to the ground with only foundation being rock piers with rubble/cement chinked between piers. ours has a celler (read that hole in the ground). i want to excavate under the existing house to form a basement. i have a mini-excavator and full sized backhoe. i've got to dig under, but resupport and in some places level the house. anyone have any ideas or have ever had this done. Thanks for any ideas.

Hal/WA

Posted 08-06-2003 at 17:54:58
[Reply] [No Email]Some friends of mine did it with their old farm house back in the 60's. All the digging was done by hand, the dirt was carried out with wheelbarrows and they mixed the concrete with an old, fairly large concrete mixer that they had set up by their aggregate pile. My friends built forms in areas, poured them in lifts and then moved the forms to other areas when the concrete had set up.

It was a tremendous amount of work. It took the 3 of them all summer to do and the digging was relatively easy as they hit very little rock. They more or less had to do something, because the old foundation, or lack thereof was falling apart and sinking and the house was being damaged structurally. They ended up with a nearly full basement, but had lots of problems with water leaks and couldn't use it for living space. But the house became properly supported again and they no longer had trouble with freezing pipes or mice. The project didn't cost them all that much, but I would guess those guys labor would have been a huge bill if they hadn't done it themselves. The house is still there and looks fine from the road.

They always said that they wished they had used delivered concrete from a pre-mix truck and done one whole wall at a time. This would have cost more, but would have been much quicker and would not have had the problems of the many small pours. It was very easy to see where one pour ended and another started and this contributed to the leakage. They also wished they had put in French drains to a drywell.

Another good way of doing such a job would be with concrete blocks. But any way you look at it, it is going to be a huge amount of work. Good luck!

Mike D.

Posted 08-06-2003 at 19:37:35
[Reply] [No Email]Whew, that sounded brutal. I used block on both of my houses. Both were water tight afterward. I put in a deep gravel base with perferated drain pipe that led to a submersible sump pump in both basements floors.I poured a concrete slab with steel. No cracks for over 20 years now. We have a woodstove, freezer, and washing machine in the basement of our farm house. The only time it flooded was when we were without power during a hurricane, all the basements in the area flooded then. I would build again with block in a heartbeat. If you need a more solid wall you can simply slop pour concrete into the block voids. Rebar is a good idea too. No formwork to build, or strip until you get to the top of the kneewall.I used a 2x6 for the outside form board and turned the pour down over the edge of the top course of block two inches. That ties the knee wall in nicely to the concrete cap. The joint between the cap and the existing wall was toothed into the old foundation and I used a fair amount of rebar in that too. Rebar is cheap, easy to use, and offers huge strengthening benefits.So, rhouston, there you have it. Good luck, and keep a steady pace. It won't take all that long, and if you are vigilant, it won't leak afterward.

another thing

Posted 08-06-2003 at 11:01:57
[Reply] [No Email]When you form the piers for any column work do yourself a favor and put steel in that pour too. I like to use 3 pieces of 1/2" rebar about a foot long each. I make an 'H' out of the with the cross piece laying on top of the other two. This makes a nice reinforecement for any future load you may put on the new column. Most pier footings are o.k. being 24" X 24" by 12" deep. On lighter bearing columns I wouldn't be hesitant to pour them 8" using that 'H' in the bottom third. Hope this helps some. Mike D.

done it-

Posted 08-06-2003 at 08:37:36
[Reply] [No Email] rhudson, This is not that big a deal if you are careful NOT to disturb the existing footing and bearing of the house as it sits now. Excavate 36" to the inside of the foundation walls. Make sure the soil is stable. You can do a 'home test' with a piece of rebar and an 8# maul. I have hand dug 2 basements. The first one was tough, but you learn tricks. I couldn't use heavy equipment. Too much vibration too close to an old foundation is not a good thing. You'll want to build a knee wall and pour a concrete cap that ties the knee wall into the old foundation. First one I used 8" block for the knee wall. The 2nd. basement I used 4" block and slop poured the cavities with concrete and used vertical placed rebar every 36". That made a stronger sub foundation than the first one did. Mike D.

walt

Posted 08-06-2003 at 06:57:24
[Reply] [No Email]I have seen this done, but it looked expensive. They basically set piers around the perimeter several feet away from the house, lower then the house. Then took "I" beams under the structure, jacked up the house and placed the beams on the piers. Dug it out, poured the footer/basement wall level, then set the house back down.